Ignition issue

[niveketak]

About 6 months ago my 122S broke down. The cause was the spring loaded contact in the distributor cap had disappeared, the cap was brand new when I installed it about a year and 500 kilometres previously. I had an identical brand new cap which I installed and all was well. Until yesterday afternoon when I experienced some hesitation followed by "back firing" into the carbs. I stopped, took off the distributor cap and found the situation in the attached image. Arcing from at least one post and an almost destroyed spring loaded contact.

I must be being dopey but I cannot fathom a reason for this happening, the condensor was as new as the cap but has been changed again and I have installed a black Quinton Hazel cap which was my last one. Any electrical wizards know why this would be happening or even someone whos brain is more awake than mine.

[arcturus]

Check you cap again and also feel if your coil is getting very hot.I had the same problem as you with two caps.(you have reconnected the ignition leads in the correct order?)

[niveketak]

Yes leads are on correctly and with new cap it runs smoothly. Will check the coil. What was the cause of your problem?

[arcturus]

Broken spring in the cap preventing the center to make good contact with rotor. It would run for a while and then start spluttering. The bad contact was causing the coil to over heat. New cap solved the problem until it started again with another broken spring.

[niveketak]

That may have been the case with the first one and I suppose the spring in the second one may also have broken causing the same problem although it does work it may not be strong enough to push the button out far enough as you said. The make of cap is Beru and I am fairly sure they both came from Brookhouse so I may give Simon a ring and see if there has been an issue before with them.

[Derek UK]

Beru are a reputable make but every now and then even the best companies have QC problems. The carbon should float on the spring easily if you press it in. From your picture the brush might be just a little too tight and hang up now and then. Check the the end of the spring where it attaches to the spring doesn't have a little bit sticking out which catches on the plastic down in the hole. I would run a drill or a rolled up piece of fine wet n dry down the hole too. Be absolutely sure that your rotor arm is correct, and is seated properly. The small tab inside can be poor and not a good fit in the slot on the shaft. Rotor may be wrong and too long. If this is a new one, check it carefully against the old one if you have kept it as a spare. We all do that don't we? This will then push the carbon too far into the hole and cause the spring to bind. Some caps don't fit properly because the half moon recess for the LT screw is either missing or poorly shaped. Cap locking springs must be good and snap into place properly. If one comes off the brass piece of the rotor can destroy the cap internally when it hits one or more of the plug lead connections. Lots of small things to check.
Story: After having the engine stop due to driving into what looked like a shallow puddle which wasn't in my Vauxhall Cavalier I needed to dry off the electrics. Took the cap off to find that the ignition had been working fine without a carbon brush. It was happily running on just the spring. It then drove around happily for a few more days before I got a new cap.

[Ron Kwas]

Nive;

That Brush looks a bit crumbly, but other then that, not too worse for wear...if it is spring-loaded when checked, so that it makes a good contact with Rotor...that doesn't bother me so much. If an earlier one "dissappeared", I would have loved to do a failure analysis on that...

...but looking closer at the picture, it seems to me from the carbon tracking, that the easiest airgap for the HV to make the jump from Rotor not to (brass) Cap-station, as it should be, was to the Cap surface, then along the surface, to the station, and this does bother me as it is an indicator that the Rotor-end, to Cap-station was not the minimum, as it typically is, and when all things are right...this is an indication of something very wrong dimensionally (or possibly just positionally!), and this promoted the arc occurring to the Cap surface as it has clearly done here, and not to the Cap-station as it should (not to mention that lots brush dust and other dust debris which is clearly visible, helped with this!...I guess I did mention it!).

BTW...I don't know if BERU and Bosch Caps and Rotors interchange.

Suggestions:

1. Check Rotor dimensions against a known good rotor!
2. Clean under Dist Cap yearly as a part of standard maintenance to prevent HV leakage and carbon tracking.
3. Carefully inspect currently available replacement parts! chinatrash is pervasive!

See also: http://www.sw-em.com/Check_Your_Dist..._Cap_Brush.htm

Cheers

[142 Guy]

Legitimate back firing through the carbs (as opposed to the more common misfire) is uncommon and is typically a sign that the ignition timing is really advanced or really retarded. The back fire is caused by ignition occurring before the intake valve is fully closed (really advanced) or as the intake starts to open (really retarded). A problem with the condenser will not cause the ignition timing to change leading to back fire, so that is not the cause of the back fire issue.

Back fire can be caused by the valve timing being really out; but, that seems unlikely in these circumstances. If the distributor came loose and rotated that can cause the timing to alter leading to back fire. However, given the evidence inside your cap distributor cap, I suspect that the back fire may have been cause by the distributor rotor arcing to the contact for an adjacent cylinder rather than the correct cylinder.

I marked up your photo of your cap. In the areas circled in color there looks to be residue on the inside of the cap that appears to have metallic particles in it. If this is correct and not a visual illusion then it suggests, as Ron Kwas has mentioned, that there a mechanical fit issue which may be leading to wear. If those particles are metallic you could have some 'rotor or cap out of position issue' combined with the metallic contamination leading to flashover to the incorrect post (and a misfire).

My university friend from long ago had an Amazon and as I recall when doing a tune up you had to be specific on the year of the engine because there was a change in the distributors during the Amazon's production run. The last time I saw that particular Amazon was 40+ years ago so I can't remember the details - whether the caps and rotors could be physically interchanged; but, not work correctly or whether the differences between the early and late distributors was so distinct that you could not fit the early cap / rotor to a late distributor or vice versa.

The inside of your cap suggests some mechanical damage to the rotor or cap that might be caused by the incorrect cap, incorrect rotor or both for your particular distributor. I suggest that you check to make sure that you have the correct cap and rotor for your particular distributor. I will hazard a guess that you are not the original owner of your 122. Is it possible that you have an early car with a late distributor that has been fitted as a replacement?

[Ron Kwas]

142G;

The issue that I am aware of with early/late Distributors is related to the two-piece vs one-piece Points. With the later, the through-hole for the points connection did not require the partial circular clearance cut-out in the Cap base as the earlier one-piece points required...that suggests to me an early Cap and Rotor can be fitted to a later Dist, with no fit issue, but not the other way around!
You could even modify a later Cap by grinding in that clearance, and fit it to an early Dist...it's not that huge a deal...but what glares at me immediately is where it was arcing to...(and all the dust in there...)

Cheers

[142 Guy]

Originally Posted by Ron Kwas

142G;

The issue that I am aware of with early/late Distributors is related to the two-piece vs one-piece Points. With the later, the through-hole for the points connection did not require the partial circular clearance cut-out in the Cap base as the earlier one-piece points required...that suggests to me an early Cap and Rotor can be fitted to a later Dist, with no fit issue, but not the other way around!
You could even modify a later Cap by grinding in that clearance, and fit it to an early Dist...it's not that huge a deal...but what glares at me immediately is where it was arcing to...(and all the dust in there...)

Cheers

Since it has been 40+ years I will defer to your more recent experience. I thought that there was some issue with the height of the rotor or height of the cap that could cause a conflict; but, that might have been on a different distributor on a different Volvo.

The presence of all that dust (or whatever that residue is) still makes me think that there must have been some kind of mechanical interference to cause all that debris. Is it possible for there to be a problem with the rotor that is preventing it from seating properly on the distributor shaft?